Mailman - Mailman is free software for managing electronic mail discussion and e-newsletter lists.
WP Mailster - WP Mailster enables you to run a listserv-like email discussion list on your WordPress site.
Mailman 3 - Dedicated Mailman 3 installation. Unlimited lists/configuration. Free subdomain at mailman3.com. Dedicated support for list admins.
Listeron - An email address for your group. Discuss. Debate. Organise. All with email.
MailChimp - MailChimp is the best way to design, send, and share email newsletters.
Sendy - Sendy is a self hosted newsletter app that sends emails 100x cheaper via Amazon SES